1. Field of the Invention
The invention relates in general to solid freeform fabrication and, in particular, to a method of producing an improved downward facing surface condition on parts produced by selective deposition modeling techniques.
2. Description of the Prior Art
Recently, several new technologies have been developed for the rapid creation of models, prototypes, and parts for limited run manufacturing. These new technologies can generally be described as Solid Freeform Fabrication, herein referred to as xe2x80x9cSFFxe2x80x9d. In SFF, complex parts are produced from a modeling material in an additive fashion as opposed to traditional fabrication techniques, which are generally subtractive in nature. For example, in traditional fabrication techniques material is removed by machining operations or shaped in a die or mold to near net shape and then trimmed. In contrast, additive fabrication techniques incrementally add portions of a build material to targeted locations, layer by layer, in order to build a complex part. Generally, SFF technologies such as stereolithography and the like utilize a computer graphic representation of a part and a supply of a building material to fabricate a part in successive layers. The building material is typically a powder, liquid, or gas. SFF technologies have many advantageous over conventional manufacturing methods. For instance, SFF technologies dramatically shorten the time to develop prototype parts. They also eliminate the need for complex tooling and machining associated with conventional manufacturing methods. In addition, SFF technologies substantially eliminate the production of waste material compared to conventional manufacturing methods.
One category of SFF that has recently emerged is Selective Deposition Modeling, herein referred to as xe2x80x9cSDMxe2x80x9d. In SDM, which is also referred to as solid object imaging, a solid modeling material is physically deposited in successive fashion to form an object. In one type of SDM technology the solid modeling material is extruded as a continuous filament through a resistively heated nozzle. In yet another type of SDM technology the solid modeling material is jetted or dropped in discrete droplets in order to build up a part. Often, a thermoplastic material having a low-melting point is used as the solid modeling material, which is delivered through a jetting system such as those used in the ink jet printers. One type of SDM process utilizing ink jet print heads is described in, for example, U.S. Pat. No. 5,555,176 to Menhennett, et al.
Although all SFF methods have many advantages compared to conventional fabrication methods, they also have inherent problems routed in the layer by layer building process. One of the most fundamental problems associated with SFF processes is the adverse effects resulting from gravitational forces that undesirably act on a part during the build process. All SFF processes must deal with gravitational forces. For example, most downward facing surfaces built by SFF processes need to be supported in order to stabilize the part during the building process. There have been many attempts to counter the undesirable effects of gravity on SFF methods, however, with less than optimal results.
One method of countering the gravity problem is to utilize dissimilar materials in the building process. In one approach a dissimilar material is utilized to produce the support structures that support the part during the build process. For example, two different solidifying materials can be selectively deposited in a layer by layer process, one material for building the part and the other material for building the support structure. Ideally, the materials are carefully selected to order to establish a weak bond joint at their juncture such that the application of an applied force separates the support structure from the part along the joint. For example, this approach is described in U.S. Pat. No. 5,617,911 to Sterett et al. Objet Geometries Ltd., in Rehovot, Israel, is currently developing this approach in conjunction with photopolymer build materials. In another approach the materials are selected such that the material comprising the support structure has a lower melting point than that of the part, and after forming, the temperature of the composite is raised in order to melt out the support structure. This type of approach is described in, for example, U.S. Pat. No. 5,141,680 to Almquist et al. Undesirably, however, the complexity of the material delivery systems is doubled in these approaches in order to account for the delivery of two dissimilar materials.
In yet another approach, a removable support material is deposited in particulate form, such as a powder, that is energized so as to fuse to form the part, with the un-fused powder acting as the support structure. This type of approach is described in, for example, U.S. Pat. No. 5,252,264 to Forderhase et al. Undesirably, however, this approach is limited for use with sintered powder materials and is generally unsuitable in applications utilizing flowable solid modeling materials to build parts.
Another attempt to solve the gravity problem is to provide for the rotation of the part about any axis while the build material is being deposited. This approach is described in, for example, U.S. Pat. No. 6,080,343 to Kaufman et al. Under this approach, the part can be theoretically positioned for optimal alignment with gravity whenever the build material is deposited. Although this approach can eliminate the need to provide a substantial amount of support structures, it cannot eliminate them all, particularly when producing highly complex structures. In addition, integrating a rotational system into an SDM process requires sophisticated equipment, sophisticated controls, and highly trained operators. Thus, rotational SDM systems are often impractical for use in most industries because of their complexity and cost.
Another group of solutions to the gravity problem is to produce structural supports at the same time, and from the same material, as that used to produce the part. The supports are then physically removed after the deposition building process is completed. One such approach produces thin needle like support columns or webs to provide support for downward facing surfaces of the part. For example, this approach is described in U.S. Pat. No. 5,141,680 to Almquist et al. In another approach, break surfaces are established by providing perforations or voids along the locations where downward facing surfaces are to be established. This approach is described in, for example, European Patent Application No. 0655317A1published May 5, 1995. In either approach, it is necessary to forcibly remove the support structures after the SDM building steps are completed. Although these solutions only require the deposition of a single build material, they produce undesirable downward facing surfaces that are rough and jagged. Attempts to improve the appearance of these surfaces have proven problematic because the support structures are strongly fused with the underlying part at their juncture with the downward facing surfaces. Currently, there is no known way to precisely control the surface condition at these junctures during or after severance. After separation, manual cleanup such as scraping, filing, and the like, is often needed in order to improve the appearance of the downward facing surfaces. Undesirably, however, such rework does not achieve the same smoothness and detail as is achieved in forming the upward facing surfaces. As a consequence of the poor surface quality of downward facing surfaces, the parts must be oriented with their most important surfaces facing up prior to being formed by the SDM process. This has proven to be a significant drawback in producing objects under conventional SDM processes.
Thus, there is a need to provide an SDM process capable of establishing downward facing surfaces that have the same surface quality and detail as upward facing surfaces. There is also a need to provide an SDM process that can produce the same quality surface finish on both upward and downward facing surfaces by the deposition of a single build material. There is also a need to provide such an SDM process capable of being performed by a conventional SDM machine without a significant amount of modification. In addition, there is a need to provide an SDM process requiring a minimal amount of training, experience, and hands-on supervision by its operators. These and other difficulties of the prior art have been overcome according to the present invention.
The present invention provides its benefits across a broad spectrum of SFF processes. While the description which follows hereinafter is meant to be representative of a number of such applications, it is not exhaustive. As those skilled in the art will recognize, the basic methods taught herein can be readily adapted to many uses. It is intended that this specification and the claims appended hereto be accorded a breadth in keeping with the scope and spirit of the invention being disclosed despite what might appear to be limiting language imposed by the requirements of referring to the specific examples disclosed.
It is one aspect of the present invention to provide a method of creating an object by SDM techniques whose downward facing surfaces exhibit superior quality and detail compared to downward facing surfaces created by conventional SDM techniques.
It is another aspect of the present invention to provide a method of creating an improved downward facing surface on an object that is severable from a support structure wherein the object and support structure are formed by SDM techniques dispensing a single build material.
It is yet another aspect of the invention to provide a method of establishing a separation zone or cold weld joint in an object formed by SDM techniques wherein the object can be precisely severed along the joint.
It is a feature of the present invention to establish a separation zone in an object formed by an SDM process by selectively dispensing a single phase change material to a plurality of target locations. The separation zone, or cold weld joint, is established by selectively dispensing the phase change material such that the outer surface temperature of the dispensed material is below the flowable temperature of the material when striking the target locations residing in the separation zone. This assures that the dispensed material has insufficient energy to integrally fuse with material adjacent the target locations.
It is another feature of the present invention to establish a first portion and a second portion of an object severably attached along a separation zone formed by the process mentioned above. The first portion and the second portion are established by selectively dispensing the phase change material such that the internal volume temperature of the dispensed material is equal to or greater than the flowable temperature of the material when striking target locations residing in the first and second portions. This assures that the dispensed material has sufficient energy to integrally fuse with the material that is adjacent to the target locations.
It is yet another feature of the present invention to provide an SDM process as discussed above wherein the first portion of the object is a support structure for the second portion, and upon separation of the first and second portions along the separation zone a desired surface is revealed on the second portion. Upon separation the second portion becomes the resultant product formed by the method.
It is still yet another feature of the present invention to provide an SDM process as discussed above wherein upon separation of the first and second portions along the separation zone, a desired surface is revealed on both portions thereby establishing mirror image parts.
It is still yet another feature of the present invention to provide an SDM process as discussed above wherein the phase change material is dispensed in discrete droplets from at least one ink jet print head at a temperature at or above the flowable temperature of the material, and the temperature of the droplets is regulated as they cool in flight. One manner of regulating the temperature of the droplets in flight is by adjusting the distance between the ink jet print head and the target locations, another is by altering the size of the droplets when dispensed, and yet another is by altering the ambient temperature in which they travel.
It is an advantage of the present invention that an improved downward facing surface is established on parts made by the SDM process resulting from the creation of the separation zone or cold weld joint along the object. The surface is improved by having significantly clearer resolution, smoothness, and definition as compared to downward facing surfaces created by conventional SDM processes.
It is another advantage of the present invention that manual cleanup operations such as scraping and filing are no longer needed on downward facing surfaces created by SDM processes that dispense a single phase change material for both the resultant product and the support structure.
It is yet another advantage of the present invention that the improvement in the appearance and quality of downward facing surfaces formed by the SDM process can be achieved without dispensing dissimilar phase change materials or a release agent.
Other aspects, advantages, and novel features of the present invention will become apparent from the following detailed description of the invention.